HIV-1 is the fifth leading cause of disability worldwide and the leading cause of morbidity in East and southern Africa. Recent clinical trials demonstrating the efficacy of antiretrovirals to prevent HIV-1 transmission have revolutionized the HIV-1 prevention field and provided the necessary components to make HIV-1 elimination potentially attainable. For HIV-1 serodiscordant couples, i.e. where one partner is HIV-1 infected and the other uninfected, the desire to have children often outweighs the HIV-1 transmission risk, and couples forgo condom use in order to satisfy their desired family size. We are currently conducting work in Kenya with HIV-1 serodiscordant couples to develop a coordinated, client-centered, evidence-based, risk-reduction safer conception intervention. Similar to approaches tested in Europe and suggested for couples in resource-limited settings, our combination approach includes: 1) antiretroviral therapy use by the HIV-1 infected partner, 2) pre- exposure prophylaxis use by the HIV-1 uninfected partner, 3) screening and treatment of genital tract infections in both partners, and 4) recommending unprotected sex only during peak fertility days of a woman's menstrual cycle (i.e. timed unprotected sex). Through formative work, however, we have identified an important gap in the feasibility of practicing timed unprotected sex that mHealth tools are perfectly suited to address. In this proposal, we aim to enhance our safer conception intervention by developing novel mHealth tools that will improve women's accuracy in identifying peak fertility periods and clinician-patient communication about safer conception and practicing timed unprotected sex. With an mHealth-experienced team of US and Kenyan HIV-1 prevention, reproductive health, and technology experts, we will 1) use simple message service (i.e. SMS or text message) surveys to determine fertility awareness methods that are most feasible for Kenyan women in HIV-1 serodiscordant partnerships to monitor, 2) develop an ovulation prediction algorithm and a safer conception tablet-based application that draws on SMS survey data to identify peak fertility days and feeds this prediction into individualized safer conception SMS messages and 3) pilot the novel mHealth tools, in combination with highly effective HIV-1 prevention strategies, among 40 HIV-1 serodiscordant couples with immediate fertility intentions to determine uptake and continued utilization of safer conception strategies and rates of condom use, pregnancy, and HIV-1 transmission. Our focus on improving the practice of timed unprotected sex is novel but fills a very important gap. While developed for HIV-1 serodiscordant couples in the Kenyan setting, each component could also be used by any African couples struggling with fertility complications. With our international, interdisciplinary team, we will additionally be able to build capacity among our local Kenyan research colleagues who have been managing mHealth projects for the past three years and are now poised to acquire new skills in application design, development and testing, and become leaders in mHealth research in Kenya.